Channel Quality Index Determination

ABSTRACT

A method of a transceiver arranged to operate in a cellular communication system comprising cells is disclosed. The method comprises receiving a transmission from a first cell; determining an interfering signal and its occupation in time and/or frequency; determining reduced values in the received signal corresponding to the occupation in time and/or frequency of the interfering signal; and measuring a quotient between desired signal and non-desired signal of reference symbols of the received signal. A channel quality index, CQI, is formed taking into account reduction of values performed at the reducing, and the CQI is reported to the communication system. A transceiver and computer program for the same are also disclosed.

RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.14/238,221, filed 11 Feb. 2014, which was the U.S. National Stage ofInternational Application No. PCT/EP2012/063178 filed on 5 Jul. 2012,which claims priority to U.S. Provisional patent Application Ser. No.61/525,266 filed on 19 Aug. 2011 and European Patent Application SerialNo. 11177396.6 filed 12 Aug. 2011, the disclosures of all of which areincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention generally relates to a method of providing aChannel Quality Index report, and a transceiver and computer programadapted therefore.

Abbreviations

3GPP 3^(rd) Generation Partnership Project

LTE 3GPP Long Term Evolution

HSPA High-Speed Packet Access

ARQ Automatic Repeat request

HARQ Hybrid ARQ

CQI Channel Quality Index

SNR Signal-to-Noise Ratio

SIR Signal-to-Interference Ratio

SINR Signal-to-Interference-and-Noise Ratio

BLER Block Error Rate

MCS Modulation and Coding Scheme

UL UpLink

DL DownLink

ABS Almost Blank Subframe

RE Resource Element

CRS Common Reference Symbol

ID Identity

IC Interference Cancelling

WWAN Wireless Wide Area Network

USB Universal Serial Bus

BACKGROUND

Cellular system optimized for mobile broadband such as, LTE and HSPA,uses link adaptation and HARQ. These functionalities are introduced forimproved throughput performance both from a link and system perspective.In link adaptation, the terminals need to estimate the current radioperformance and feedback that information to the network as a CQI. Thenetwork node (scheduler) then adapts the MCS. HARQ is then introducedfor robust performance, and used for fast retransmission of erroneousdecoded blocks. In a typical channel scenario, for optimisedperformance, a first transmission BLER around 10% is close to optimalfrom link perspective, and the scheduler is working to choose MCS basedthe CQI and BLER target.

Traditionally, CQI is solely based on SNR of the received signal.Internally generated decisions like adaptation/nulling/affecting of softvalues to known interference are not taken into account, and thereby theCQI reported will not correctly describe the current decodingperformance, and the reported CQI may be too optimistic. Thus, this willreduce the throughput in the system, by increasing the firsttransmission BLER, which typically should operate around 10% foroptimized performance, and thereby increasing the packet retransmissionrate. In some scheduling solutions some outer loop control is introducedin the scheduler that eventually will take such biased CQI into account,but such loop is normally slow and therefore the interference situationfor the terminal could well be changed, for instance by a handover toanother cell, before caution is taken by the controller. Hence optimizedperformance will not necessarily be reached using such outer loop BLERcontrol compensation

Thus, the terminal estimates the CQI and reports it to the cellularsystem, and all reported CQls are important for the cellular system forworking efficiently.

WO 2005/000568 A2 discloses a method for biasing signal-to-interferenceratio (SIR) to generate channel quality indicator (001) includingmeasuring the packet error rate (PER) of a received signal and comparingthe PER to a to the target PER to generate a correction term. Thecorrection term is combined with the SIR estimation of a referencechannel to generate a CQI. The CQI is reported to a transmitter toadjust signal configurations, such as code rate, modulation type, numberof codes, power offset.

However, in modern cellular systems, numerous “tricks” are applied, bothin the terminals and in the base stations, to improve performance. Someof these tricks may cause the estimated/reported CQls to give animproper view of the actual channel qualities, which then may imply thatthe cellular system does not work that efficiently as intended. It istherefore a desire to provide a CQI that better reflects channelquality.

BRIEF SUMMARY

An object of the invention is to at least alleviate the above statedproblem. The present invention is based on the understanding that“reduced” values of received signals at the terminal side, gives adifferent effective code rate than that of the originally assigned andused code rate. This may impact the actual channel quality. Theinventors have found that, at least for an overall system efficiency, aCQI reported from a terminal to the cellular system should reflect theactual channel quality, and therefore here provide a set of solutionsfor an improved CQI reporting.

Here, “reduction” includes deletion, nulling, suppression, or otheradaptation of received values that are known or suspected to beinfluenced by an interferer, where the reduction can be an activemeasure by deleting, nulling suppressing, etc. the soft values in thereceiver or in subsequent processing circuits, or the reduction can bethe cause of the interference where the soft values are so corrupt thatthey cannot be properly used for processing in the transceiver orsubsequent processing circuits. In the following disclosure, the terms“reduced” and “reduction” will be used about the soft values of dataRes, which is to be interpreted as reducing the influence of the signalvalue in signal processing performed on the received signal, e.g. atdecoding. The reduction can thus be total, i.e. the value is set tozero, or partial, i.e. the value is given an amount implying lowerimpact.

According to a first aspect, there is provided a method of a transceiverarranged to operate in a cellular communication system comprising cells.The method comprises receiving a transmission from a first cell;determining an interfering signal and its occupation in time and/orfrequency; determining reduced values in the received signalcorresponding to the occupation in time and/or frequency of theinterfering signal; measuring a quotient between desired signal andnon-desired signal of reference symbols of the received signal; forminga channel quality index, CQI, based on the measured quotient and anamount of determined reduced values; and reporting the CQI to thecommunication system.

According to a second aspect, there is provided a method of atransceiver arranged to operate in a cellular communication systemcomprising cells. The method comprises receiving a transmission from thefirst cell; measuring a quotient between desired signal and non-desiredsignal of reference symbols of the received signal; determining aninterfering signal and its occupation in time and/or frequency;determining reduced values in the received signal corresponding to theoccupation in time and/or frequency of the interfering signal;calculating effective code rate with regard to the reduction;calculating an adapted capacity based on the reduction; mapping thecapacity or adapted capacity to a channel quality index, CQI; andreporting the CQI to the communication system.

The method may further comprise, after the step of measuring a quotient,mapping the measured quotient to an estimated capacity; and determining,based on the capacity, whether any reduction is needed to be taken intoaccount, wherein if reduction is determined to be needed to be takeninto account, performing the steps of determining reduced values in thereceived signal, calculating effective code rate and calculating anadapted capacity based on the reducing, and if reduction is notdetermined to be needed to be taken into account, omitting these steps.

For the methods of the first and second aspects, the cellular system mayfurther comprise a second cell and the second cell covers essentiallythe whole coverage area of the first cell, wherein the second cell maybe arranged to transmit at least one subframe simultaneously with thefirst cell scheduling transmission, wherein the determination of theinterfering signal comprises determination of presence of symbolstransmitted during said at least one subframe from the second cell. Thesecond cell may be arranged to transmit at least one subframe comprisingno data symbols and only reference symbols such that the first cell isenabled to schedule transmission, and wherein the interfering signal tobe taken into account for determining reduced values are correspondingto the reference symbols transmitted from the second cell.

For the methods of the first and second aspects, the determination ofthe interfering signal may comprise determining a spur signal internallygenerated in the transceiver.

For the methods of the first and second aspects, the forming of the CQImay further be based on position of occupation in time and/or frequencyof the determined reduced values in the subframe. The forming of the CQImay further be based on allocation size of the determined reducedvalues.

According to a third aspect, there is provided a transceiver arranged tooperate in a cellular communication system comprising cells. Thetransceiver comprises a receiver arranged to receive a transmission froma first cell; an interference monitor arranged to determine aninterfering signal and its occupation in time and/or frequency; areduction determination circuit arranged to determine reduced values inthe received signal corresponding to the interfering signal; a signalmeasuring circuit arranged to measure a quotient between desired signaland non-desired signal of reference symbols of the received signal; aprocessor circuit arranged to form a channel quality index, CQI, basedon the measured quotient and an amount of reduced values performed atthe reducing; and a transmitter arranged to transmit a report of the CQIto the communication system.

According to a fourth aspect, there is provided a transceiver arrangedto operate in a cellular communication system comprising cells. Thetransceiver comprises a receiver arranged to receive a transmission fromthe second cell; a signal measuring circuit arranged to measure aquotient between desired signal and non-desired signal of referencesymbols of the received signal; a reduction determination circuitarranged to determine reduced values in the received signalcorresponding to interfering symbols of the interfering transmissionfrom the first cell to perform the determination of the reduction, and aprocessing circuit arranged to calculate effective code rate with regardto the determined reduction, and calculate an adapted capacity based onthe determined reduction, wherein the processing circuit is furtherarranged to map the capacity to a channel quality index, CQI; and atransmitter arranged to transmit a report on the CQI to thecommunication system. The processing circuit may further be arranged tomap the measured quotient to an estimated capacity, and be arranged todetermine, based on the capacity, whether any determination of reductionis needed to be taken into account, wherein if reduction is determinedto be needed to be taken into account, the processing circuit isarranged to enable the reduction determination circuit to determinereduced values in the received signal, and if reduction is notdetermined to be needed to be taken into account, be arranged to disablethe reduction determination circuit, wherein the estimated capacity fromthe mapping of the measured quotient is used as the capacity and thecalculation of an effective code rate is omitted.

For the third and fourth aspects, the cellular system may furthercomprise a second cell and the second cell covers essentially the wholecoverage area of the first cell, wherein the second cell may be arrangedto transmit at least one subframe simultaneously with the first cellscheduling transmission, wherein the determination of the interferingsignal may comprise determination of presence of symbols transmittedduring said at least one subframe from the second cell. The second cellmay be arranged to transmit at least one subframe comprising no datasymbols and only reference symbols such that the first cell is enabledto schedule transmission, and wherein the interfering symbols to bedetermined as reduced by the reduction determination circuit arecorresponding to the reference symbols from the second cell.

For the third and fourth aspects, the reduction determination circuitmay further be arranged to determine reduced values corresponding to aspur signal internally generated in the transceiver.

For the third and fourth aspects, processor circuit may further bearranged to base the CQI on position of occupation in time and/orfrequency of the determined reduced values in the subframe.

For the third and fourth aspects, the processor circuit may further bearranged to base the CQI on allocation size of the determined reducedvalues.

According to a fifth aspect, there is provided a computer programcomprising computer executable instructions, which when executed by aprocessor of a transceiver is arranged to cause the transceiver toperform the method according to any of the first or second aspects.

Other objectives, features and advantages of the present invention willappear from the following detailed disclosure, from the attacheddependent claims as well as from the drawings. Generally, all terms usedin the claims are to be interpreted according to their ordinary meaningin the technical field, unless explicitly defined otherwise herein. Allreferences to “a/an/the [element, device, component, means, step, etc]”are to be interpreted openly as referring to at least one instance ofsaid element, device, component, means, step, etc., unless explicitlystated otherwise. The steps of any method disclosed herein do not haveto be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings.

FIG. 1 illustrates a cellular communication system comprising cellswherein the whole coverage area of first cell of one level isessentially covered by a second cell of another level.

FIG. 2 illustrates a number of subframes transmitted by the second cell.

FIG. 3 illustrates a receiver in which internal interference is caused.

FIG. 4 illustrates a number of subframes received from the first cell,and internal interference caused as illustrated in FIG. 3.

FIG. 5 is a flow chart illustrating a method according an embodimentaccording to a first approach.

FIG. 6 is a flow chart illustrating a method according to an embodimentaccording to a second approach.

FIG. 7 is a flow chart illustrating a method according to an embodimentaccording to the second approach.

FIG. 8 is a block diagram schematically illustrating a transceiveraccording to embodiments.

FIG. 9 is a block diagram schematically illustrating a cellular deviceaccording to embodiments.

FIG. 10 is a diagram illustrating mapping of channel capacity and SNRfor different modulation schemes.

FIG. 11 schematically illustrates a computer-readable medium comprisinginstructions, which when executed on the illustrated processor arearranged to implement any of the methods illustrated in FIGS. 5 to 7.

DETAILED DESCRIPTION

In some radio scenarios/cases, the terminal could experience significantinterference on certain received symbols/resource elements, using theterminology of LTE but similar principle applies for other systems. Onesuch scenario is Heterogeneous Network (HetNet) scenarios wheremacrocells and picocells are mixed, as illustrated in FIG. 1, whichillustrates two cells 100, 102 each operated by base stations 104, 106,and in which a terminal 108 is operating. For improved UL performance itis sometimes better for a terminal to be connected to the picocellrather than the macrocell even if the DL is significantly, e.g. 10-15dB, stronger from the macrocell than from the picocell. The reason isdifferent max output power, for the macrocell in the range of 40 dBm,while for the terminal around 23 dBm. Another reason is different ULpath loss from terminal to picocell and macrocell, respectively, due todifferent distances and propagation conditions to the respective cell.To mitigate the interference problem, ABSs are introduced, i.e.subframes where the macrocell does not transmit data and hence terminalsconnected to the picocell can be scheduled. However, pilot symbols, CRS,need to be transmitted from the macrocell also in the ABS subframes.These CRS give rise to significant interference at certain Res, as isillustrated in FIG. 2. Since the terminal has detected the macrocell inthe cell search process, and thereby having information about the cellID and the Res used for CRS, this can be compensated in the terminal byreducing soft values for bits originated from these Res and interferingwith Res of the picocell containing data, and thus having impact oneffective code rate, as will be further elucidated below. Thus, in thecase a CRS of the macrocell happens to only interfere with a CRS of thepicocell, which on the other hand is a less likely situation thaninterfering with an RE of the picocell containing data, the effectivecode rate of the data transmission within the picocell is not affected.Other examples of methods that can be used are soft value scaling andcancellation. All these methods need an adjustment in the CQI. One caninterpret such approach as a simple IC receiver. The reducing of softvalues will increase the effective code rate, since reducing basicallyhave the same effect as puncturing. In the case of CRS interferencearound 9-10% of the Res are reduced and thereby increasing the effectivecode rate, seen by the terminal, by the same amount.

FIG. 3 illustrates a receiver 300 in which internal interference iscaused. The receiver 300 comprises a front-end receiver 302 connected toan antenna arrangement 303 and clocked by a local oscillator 304 using acrystal oscillator 306 as reference. The front-end receiver 302 providesits output to a low-pass filter 308, and the signal is further providedto a quantizer 310, and in the case of an OFDM signal, to a Fast FourierTransformer 311, and then on to a detector 312 and to further higherlayer processing. In this scenario, internally, i.e. in the transceiverin the terminal, generated spurs can introduce significant interferenceon certain sub-carriers, as illustrated in FIG. 3 (dotted arrow) andFIG. 4 (indicated spur frequency). This is especially the case at lowsignal levels close to the reference sensitivity level where spurs canaffect the performance. The spurs are typically generated by the crystaloscillator and harmonics can hit one or a few subcarriers in thereceived frequency band. Since the crystal oscillator frequency isknown, and also which potential harmonics that could interfere with thesome sub-carriers, one way to mitigate such interference is by reducingsoft values for bits originated from these affected Res, as illustratedin FIG. 4. Also in this case, the code rate increase is basicallyproportional to number of affected sub carriers and Res in relation tothe total amount of subcarriers and Res, respectively.

The basic concept of the invention is that the terminal determines theCQI transmitted to the network node not only based on the current SNR ofthe received signal, which for example is estimated using the CRSs, butalso based on prior knowledge of number of reduced soft values.Reduction of soft values might be needed for resource element that isseverely distorted by known interferers. In one embodiment, theinterferer is known pilot or reference symbols, or other known symbols,transmitted from an adjacent neighbouring network node that introducessignificant interference on certain resource elements, i.e. theneighbouring cell can be considered, from a signal point of view, tocover an essential part of the cell on which the terminal is camping.Here, it should be noted that the actual coverage of the cell on whichthe terminal is camping is not crucial in itself, since it is the signalenvironment at the place where the terminal is actually located, andcoverage at other positions does not technically influence the functionof the invention. Further, the term cell should be construed in view ofits function in a cellular system, where a “cell” may be divided intosectors, each working as a cell on its own. In another embodiment theknown interferer could be a spur signal internally generated in thetransceiver, that is known to interfere a certain number of sub-carrierand thereby, for improved performance, reduction of soft values for bitstransmitted on these resource elements are needed. Reduction of softvalues will affect, i.e. increase, the effective code rate and hencethis knowledge is taken into account in the CQI determination. With theproposed invention the CQI index is adapted to the current receiverperformance and thereby optimized throughput is achieved.

The concept can be used in two main approaches: doing the reduction andcalculating the CQI based on the reduction; or estimating capacity,doing reduction based on estimated capacity, re-estimating capacityafter reduction, and calculating CQI based on re-estimated capacity. Inthe first approach, the CQI is directly mapped on the made reduction,and in the second approach, the CQI is indirectly mapped on the madereduction, i.e. on the achieved capacity after reduction.

FIG. 5 is a flow chart illustrating a method where the first approach isemployed. A transmission is received 500 by a terminal from a basestation operating a first cell on which the terminal is currentlycamping. Further, a present interferer is determined 502. The interferercan for example be another cell performing transmissions occupyingfrequencies and time instants comprised in the transmission from thefirst cell. The interfering cell can for example be a macrocellspreading its transmissions over the coverage area of the first cell,which then can be considered as a picocell (or microcell or cell ofanother level, depending on used terminology for the cellular system).The interfering cell can also be a neighbouring cell, although thisproblem should have been solved by proper cell planning and frequencyallocation. Further, the interferer can be a spur generated internallyin the terminal, as described above. A combination of any of these is ofcourse possible. The determination 502 of the interferer includesdetermination of frequency and/or time occupation of the interferer. Forthe case of a spur, the interferer may be present at all times of theperiod of consideration of the determination, and on a specificfrequency due to the cause of the spur being an oscillator running thewhole period on a certain frequency. For the case of another interferingcell, the overlap may be present on certain frequencies at certain timeinstants of the period of consideration of the determination. Theinformation on when in time and where in frequency the interferer ispresent, it is possible to conclude what values of the received signalthat are hit by the interferer. Based on this, those interfered values,i.e. values that are reduced, are determined 504. Further, a quotientbetween desired and non-desired signals is measured 506. This can forexample be SNR, SIR, SINR or other type of quotient that is preferred ordevised for channel quality calculations. It should be noted that theorder of the actions 500, 502, 506 need not be in the specified order,although that of course is possible. For example, the determination 502of the interferer may be made periodically, and can thus have been madeprior the reception 500 of the transmission, i.e. the determination 502of the interferer is considered valid for several receptions 500 of thetransmission. Similarly, the measurement 506 of the quotient can be madeprior the determination 502 of the interferer, but need of course bemade after the reception 500 of the transmission. The determination 502of the interferer can also be made prior the reception 500 of thetransmission, and for each transmission. The latter can have theadvantage of the transmission not “interfering” the determination of theinterferer. The actions 500, 502, 506 can also be performed essentiallysimultaneously.

When reduction of interfered values is determined 504, and the quotientis measured 506, a CQI is formed based on the quotient and the amount ofreduced values. Thus, the CQI takes into account the signal qualitybased on the measured quotient, but also takes into account any changein effective code rate based on the performed determination of reductionof values. The CQI is then transmitted 510 to the base station of thecamping cell as a CQI report.

FIGS. 6 and 7 are flow charts illustrating methods where the secondapproach is employed. FIG. 6 illustrates a basic embodiment to providean improved CQI report according to the second approach, and FIG. 7illustrates an embodiment with optional conditional determination ofreduction of interfered values based on a preliminary determinedcapacity. For actions of the respective embodiments being mutuallysimilar, the same reference numerals are used for convenience ofcomparison of the embodiments.

For the basic embodiment, similar to the embodiment demonstrated withreference to FIG. 5, a transmission is received 600, a quotient ismeasured 602, e.g. SNR, SIR or SINR, the interferer is determined 604,and reduction of interfered values is determined 606. Based on thedetermined reduction 606, an effective code rate is calculated 608.Based on the effective code rate, capacity of the channel is calculated610. The calculated capacity is then mapped 612 to a proper CQI, and aCQI report is transmitted 614 to the base station. For the conditionalembodiment, similar actions of receiving 600 a transmission andmeasuring 602 a quotient are performed. Then, the measured quotient ismapped 609 to channel capacity, and then it is determined 603 whetherany reduction is needed to be taken into account. If the capacity issufficient, i.e. no reduction is needed to be taken into account, themapped capacity is in turn mapped 612 to CQI and the CQI is reported ina transmission 614 to the base station. However, if reduction is neededto be taken into account, the similar actions as demonstrated withreference to FIG. 6 are performed, i.e. determining 604 the interferer,determining reduction 606, i.e. amount of interfered values, andcalculation 608 of effective code rate. The capacity is re-calculated610′ and then the re-calculated capacity is mapped 612 to CQI and theCQI is reported in a transmission 614 to the base station. Here, itshould be noted that the action of determining 604 the interferer isillustrated to be performed only upon the conditions of neededconsideration of reduction. However, in practice, the interferer may bedetermined anyway, e.g. prior reception of the transmission or forseveral transmissions, as demonstrated with reference to FIG. 5.

In common for the approaches the terminal can on a regular basis, e.g.every subframe, estimate the quotient of the received signal. Thequotient is typically estimated using some kind of pilots or referencesymbols and the method is not limited by the invention. Based on thequotient a CQI index is determined. This is typically based on using themean value of an adjusted channel capacity over some points on thetime-frequency grid in a subframe. The capacity, in bits, can becalculated as C=BW*log2(I+Q), where BW is the bandwidth, I is the unitymatrix, and Q is a matrix representing the quotient. The adjustment ofthe capacity is for compensating for e.g. coding losses, channelestimation losses and modulation restrictions. Typically such curve maylook like FIG. 10 for different modulations. The mean value can then bemapped onto a CQI value by using table 7.2.3-1 in 3GPP 36.213specification. A control unit can then determine whether there is anydetermination of reduction of soft values needed, as of the methodillustrated in FIG. 7. The reasons for determination of reduction ofsoft values for bits/symbols transmitted on certain resource elementscan be as has been described above. Based on the number of soft valuesthat are reduced, the control unit determines how this will affect theeffective code rate. As an addition to only use the number of reducedsoft values, also the placement of the reduced values and/or allocationsize can be taken into consideration. These extra options take advanceof the code block layout on the time-frequency grid. The modified CQIvalue is determined based on the amount of reduced soft values. In oneembodiment, the puncturing can for instance be mapped to an “effectiveSIR degradation due to puncturing”, which is then used in combination tothe estimated SIR for determination of a modified CQI. Such “SIRdegradation” information can be stored in a look-up table and be basedon lab experiment earlier made. In another embodiment, the puncturingcan be mapped to symbol information degradation that is then reducedfrom the symbol information determined upon considering the need forreduction and a modified symbol information is then mapped to a modifiedCQI. Finally the terminal transmits the modified CQI to the network onregular basis, defined by parameters the terminal received duringconnection setup with the network node, or in later signalling betweenthe network node and the terminal.

An example of how a reported CQI value may change due to soft valuereduction is to assume that there are 100 data Res that transmit datasymbols, and 10 reference Res that transmit pilot symbols. Assume that10 out of the 100 data Res have strong interference from e.g. amacrocell, and that an estimated SNR from the pilot symbols is 10 dB,which corresponds to approximately an average capacity of 3 bits per RE.The terminal knows and takes the interferer into account, the capacitybecomes 90 times 3 (the non interfered Res) plus 10 times 0 (theinterfered Res assumed to have capacity 0) divided by 100 (the totalnumber of data Res), which is 2.7 bits per RE. From table 7.2.3-1 in3GPP 36.213 specification this would give us CQI 9. The uncorrectedcalculation of 3 bits per RE would give CQI 10.

FIG. 8 is a block diagram schematically illustrating a transceiver 800according to embodiments. The transceiver 800 is arranged to operate ina cellular communication system as elucidated above with reference tothe demonstrated methods. The transceiver comprises a receiver 802 and atransmitter 804 connected to some antenna arrangement comprising one ormore antennas. The transceiver 800 further comprises measuring circuitry806 which comprises an interference monitor which is arranged todetermine information about an interferer received through the receiver802, i.e. from another cell and/or an internally generated spur asdemonstrated above. The measuring circuitry 806 also comprises a signalmeasuring circuit arranged to measure a quotient between desired andnon-desired signals, as also demonstrated above. The measuring circuitry806 provides results to a processing circuit 808, i.e. a controller. Themeasuring circuitry 806 can be a part of the receiver 802, part of theprocessing circuit 808, or a separate circuit. The processing circuit808 is arranged to form a CQI, which is provided to the transmitter 804for reporting to the cellular network. The processing circuit 808 isfurther arranged to control a reduction determination circuit 810 whichis arranged to determine reduced values in the received signalcorresponding to the interfering signal, wherein the processing circuit808 may determine whether determination of reduced values is needed tobe taken into account, and enabling/disabling the function of thereduction determination circuit 810. Here, the reduction determinationcircuit 810 can be a part of the processing circuit 808, e.g.functionally integrated, or a separate circuit. The processing circuit808 forms the CQI in dependence of performed reduction of values. Thiscan be either by basing the CQI on the measured quotient and theperformed reduction, or based on a calculation of capacity, which is theresult of any performed reduction. Here, optionally, the processor isarranged to determine whether any reduction should be made at all basedon an initial calculation of capacity.

The structure demonstrated above have the capability to determine natureof the interfering signal to perform the control of the reductiondetermination circuit 810 to determine reduced values of the receivedsignal. The occupation in time and/or frequency, and also the allocationof the interferer is determined for this. This information can also beused for the forming of the CQI.

FIG. 9 is a block diagram schematically illustrating a cellular device900 according to an embodiment. The cellular device 900 can be a mobileterminal, such as a mobile phone, a WWAN module or a WWAN capabledevice. The cellular device 900 comprises a transceiver 800 as the onedemonstrated with reference to FIG. 8. The transceiver 800 providesreceived values to a decoder 902, and receives values from an encoder904 to be transmitted to the cellular network. The decoder 902 and theencoder 904 are connected to circuitry 906 for higher layer processing,which is not further elucidated here not to obscure the gist of theinvention. The cellular device 900 can further comprise a user interface908 and/or further interfaces 910, e.g. USB, IEEE 1394, or proprietaryinterfaces, for connecting to further devices.

The methods according to the present invention is suitable forimplementation with aid of processing means, such as computers and/orprocessors, especially for the case where the transceiver as depicted inFIG. 8 has signal processing implemented by programmable processingmeans, such as including a signal processor. Therefore, there isprovided computer programs, comprising instructions arranged to causethe processing means, processor, or computer to perform the steps of anyof the methods according to any of the embodiments described withreference to FIGS. 5 and 6. The computer programs preferably comprisesprogram code which is stored on a computer readable medium 1100, asillustrated in FIG. 11, which can be loaded and executed by a processingmeans, processor, or computer 1102 to cause it to perform the methods,respectively, according to embodiments of the present invention,preferably as any of the embodiments described with reference to FIGS. 5to 7. The computer 1102 and computer program product 1100 can bearranged to execute the program code sequentially where actions of theany of the methods are performed stepwise. The processing means,processor, or computer 1102 is preferably what normally is referred toas an embedded system. Thus, the depicted computer readable medium 1100and computer 1102 in FIG. 11 should be construed to be for illustrativepurposes only to provide understanding of the principle, and not to beconstrued as any direct illustration of the elements.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope of the invention, as defined by the appendedpatent claims.

1. A method of a transceiver arranged to operate in a cellularcommunication system comprising cells, the method comprising receiving asignal transmitted from a first cell; determining an interfering signaland its occupation in time and/or frequency, wherein the interferingsignal comprises one or more reference symbols transmitted from a secondcell in respective resource elements of an almost blank subframe;reducing soft bit values for bits of one or more received symbols in thereceived signal corresponding to the occupation in time and/or frequencyof the reference symbols in the interfering signal to obtain reducedvalues for the bits of the received symbols; measuring a quotientindicative of a signal quality of the received signal; forming a channelquality index, CQI, based on the measured quotient and the reducedvalues; and reporting the CQI to the communication system.
 2. The methodaccording to claim 1, wherein determining an interfering signalcomprises determining a spur signal internally generated in thetransceiver.
 3. The method according to claim 1, wherein the forming ofthe CQI is further based on position of occupation in time and/orfrequency of the reduced values in the subframe.
 4. The method accordingto claim 1, wherein forming of the CQI is further based on allocationsize of the reduced values.
 5. A method of a transceiver arranged tooperate in a cellular communication system comprising cells, the methodcomprising receiving a signal transmitted from a first cell; measuring aquotient indicative of a signal quality of the received signal;determining an interfering signal and its occupation in time and/orfrequency, wherein the interfering signal comprises one or morereference symbols transmitted from a second cell in respective resourceelements of an almost blank subframe; determining, based the interferingsignal and its occupation in time and/or frequency, a channel qualityindex, CQI, by: reducing soft bit values for bits of one or morereceived symbols in the received signal corresponding to the occupationin time and/or frequency of the reference symbols in the interferingsignal to obtain reduced values for the bits of the received symbols;calculating an effective code rate based on the reduced values;calculating an adapted capacity based on the effective code rate;mapping the adapted capacity to the channel quality index, CQI; andreporting the CQI to the communication system.
 6. The method accordingto claim 5, further comprising mapping the measured quotient to anestimated capacity, and determining whether reduction of the soft bitvalues is needed based on the estimated capacity.
 7. The method of claim6 wherein determining, based the interfering signal and its occupationin time and/or frequency, a channel quality index is performed when itis determined that reduction in the soft bit values is needed.
 8. Themethod of claim 7 further comprising determining the CQI based on theestimated capacity when it is determined that reduction of the soft bitvalues is not required.
 9. A transceiver arranged to operate in acellular communication system comprising cells, the transceivercomprising a receiver configured to receive a signal transmitted from afirst cell; a signal measuring circuit configured to measure a quotientindicative of a signal quality of the received signal; an interferencemonitoring circuit configured to determine an interfering signal and itsoccupation in time and/or frequency, wherein the interfering signalcomprises one or more reference symbols transmitted from a second cellin respective resource elements of an almost blank subframe; a reductiondetermination circuit configured to reduce soft bit values for bits ofone or more received symbols in the received signal corresponding to theoccupation in time and/or frequency of the reference symbols in theinterfering signal to obtain reduced values for the bits of the receivedsymbols; a processing circuit configured to form a channel qualityindex, CQI, based on the measured quotient and the reduced values; and atransmitter arranged to transmit a report of the CQI to thecommunication system.
 10. The transceiver according to claim 9, whereinthe interference monitoring circuit is configured to determine a spursignal internally generated in the transceiver.
 11. The transceiveraccording to claim 9, wherein the processor circuit is furtherconfigured to form the CQI based on position of occupation in timeand/or frequency of the reduced values in the subframe.
 12. Thetransceiver according to claim 9, wherein the processor circuit isfurther configured to form the CQI based on allocation size of thereduced values.
 13. A transceiver arranged to operate in a cellularcommunication system comprising cells, the transceiver comprising areceiver arranged to receive a signal transmitted from a first cell; asignal measuring circuit arranged to measure a quotient indicative of asignal quality of the received signal; an interference monitoringcircuit configured to determine an interfering signal and its occupationin time and/or frequency, wherein the interfering signal comprises oneor more reference symbols transmitted from a second cell in respectiveresource elements of an almost blank subframe; a reduction determinationcircuit configured to reduce soft bit values for bits of one or morereceived symbols in the received signal corresponding to the occupationin time and/or frequency of the reference symbols in the interferingsignal to obtain reduced values for the bits of the received symbols; aprocessing circuit configured to: calculate effective code rate withregard to the determined reduction; calculate an adapted capacity basedon the determined reduction; and map the capacity to a channel qualityindex, CQI; and a transmitter arranged to transmit a report on the CQIto the communication system.
 14. The transceiver according to claim 13,wherein the processing circuit is further configured to: map thequotient to an estimated capacity, and determine whether reduction ofthe soft bit values is needed based on the estimated capacity.
 15. Thetransceiver of claim 14 wherein, the processor circuit is configure todetermine the channel quality index based the interfering signal and itsoccupation in time and/or frequency when it is determined that reductionin the soft bit values is needed.
 16. The transceiver of claim 15wherein, the processor circuit is configure to determining the CQI basedon the estimated capacity when it is determined that reduction of thesoft bit values is not required.
 17. A non-transitory computer readablemedium comprising executable program code that when executed by aprocessor circuit in a transceiver causes the transceiver to: receive asignal transmitted from a first cell; determine an interfering signaland its occupation in time and/or frequency, wherein the interferingsignal comprises one or more reference symbols transmitted from a secondcell in respective resource elements of an almost blank subframe; reducesoft bit values for bits of one or more received symbols in the receivedsignal corresponding to the occupation in time and/or frequency of thereference symbols in the interfering signal to obtain reduced values forthe bits of the received symbols; measure a quotient indicative of asignal quality of the received signal; form a channel quality index,CQI, based on the measured quotient and the reduced values; and reportthe CQI to the communication system.
 18. A non-transitory computerreadable medium comprising executable program code that when executed bya processor circuit in a transceiver causes the transceiver to: receivea signal transmitted from a first cell; measure a quotient indicative ofa signal quality of the received signal; determine an interfering signaland its occupation in time and/or frequency, wherein the interferingsignal comprises one or more reference symbols transmitted from a secondcell in respective resource elements of an almost blank subframe; reducesoft bit values for bits of one or more received symbols in the receivedsignal corresponding to the occupation in time and/or frequency of thereference symbols in the interfering signal to obtain reduced values forthe bits of the received symbols; calculate an effective code rate basedon the reduced values; calculate an adapted capacity based on theeffective code rate; map the adapted capacity to the channel qualityindex, CQI; and report the CQI to the communication system.